Service valves are used in refrigerant systems to conveniently, add and remove refrigerant. Referring to FIG. 13, a common type of service valve is the front-seat valve 730. An example of such a valve is shown in U.S. Pat. No. 4,644,973 to Itoh et al. Front seat valve 730 contains a charge port 735 through which the installation/service technician can gage the system pressure, evacuate the system, or add refrigerant charge to the system. Front seat valve 730 has a front seat 744 that seals against a mating portion of valve body 732. Charge port 735 is equipped with a valve core 737, which prevents refrigerant from escaping charge port 735 until a stem 738 of valve core 737 is depressed by the service hose connection. Valve core 737 is sealed with elastomeric seals which can lose their sealing characteristics over time. When connected to a service hose, a flow path through charge port 735 is opened and the system can be accessed. The volumetric flow rate of gas, into or out of the system, is restricted by this generally small flow path. Therefore, the time required to service the system is negatively increased due to the size.
Another well-known charge port configuration is found on the more costly and bulky back-seat service valve 780, shown in FIG. 14. The back-seat valve has both a front seat 794 and a back seat 791 which seal against sealing surfaces of valve body 783. Front seat 794 works the same way as front-seat valve 730. Back-seat valve 780 offers an isolated charge port without employing a valve core, therefore it must be capped (not shown). A valve stem 787 in this design is back-seated (at 791) during normal operation. Back seat 791 is typically a metal-to-metal seal and offers greater leak prevention than that of front seat valve 730. In the back-seated position, a charge port 785 is sealed off, or isolated, from the system. Thus, the charge port cap can be removed while valve 780 is back-seated without any concern of refrigerant escaping the system. Once the service hose is attached to charge port 785, valve's stem 787 is mid-seated so that charge port 785 is in communication with the system. Servicing the system (evacuation and charging of refrigerant) can be executed with a higher volumetric flow rate due to the lack of restriction in the flow path (no valve core). This larger flow path results in a shorter service time. However back-seat valve 780 is bulky and expensive to manufacture. Plus valve stem 787 has to be manipulated in order to access charge port 785, which is inconvenient for the end user.
Other prior art service valves utilize valve stems that have a component which must be rotated in order to add or remove refrigerant. For example, in many designs the valve stem is threadedly connected to the charging hose assembly in order to add refrigerant. The valve stem is also threadedly connected to the service valve body. Since the valve stem has to be rotated in order to open the service port, the stem may undesirably rotate relative to the service hose. This can be problematic since the sealed threaded connection between the valve stem and charging hose assembly may come unsealed. It is helpful to provide a valve stem that doesn't rotate when it is being opened and closed.
Other prior art service valves have valve stems that can be completely removed from the service valve. If this happens, then a complete loss of refrigerant from the system will occur. This, of course, is quite undesirable not only from an end user vantage point, but also from an environmentally friendly one. For example, the component, which typically is the valve stem, needs to be unseated from the valve body in order to add and remove refrigerant from the system. Prior art designs do not prevent the complete removal of this component and a complete loss of system refrigerant will occur when this happens.